The most I've done is 11lbs and it was tight mashing. I split my sparge volume in half for batch sparging. It works out to about the same volume as the mash. But 11lbs is enough if you don't like bigger beers anyway...

Came across a never used 5-gallon Rubbermaid drink cooler. Going to convert it to a mash tun. I'm not a fan of big, high alcohol beers so I'm thinking I should be OK with this for AGs.

What can I max out with the grain bill and water? I've read that about 10lbs of grain and an original gravity in the 1.060 neighborhood.

I have both a 5 and a 10 gallon and the 5 gallon will hold about 12 pounds with 1.25Q/pound mash..Unless you effeciency is 85% or higher I would get a 10 gallon cooler IMO. Even if you do not like bigger beers, it will not hurt anything except maybe 15 more dollars. Also if you want to do a 10 gallon batch in the future you will be all ready.

Not to continue this and go in another direction, OK, I guess it will...

What factors really determine your efficiency? Or asked another way, what makes on system more efficient than another?

I assume that the more efficient your system is, the less grain you may need to reach you target O.G.?

As I head into AG from extract, I'm confused and complexed! But I was the same heading into my first every batch and then everythign clicked.

Its your thread, take it in any direction you like. IMO, efficiency starts peaking when you've become comfortable with your setup and things are dialed in. This unforunately takes some time and some off the mark batches. I am happy with consistently getting 80% but it could be better (or worse). Doing what you feel the most comfortable with is more important than doing whatever it takes to get closer to 100% efficiency (not likely). Once you're comfortable and things are dialed in, you'll be getting good efficiency every time. You're correct that the better your effeciency is, the less grain you'll need to hit your target OG. There are many, many variables though. Like how your efficiency can lower as you raise your target OG. Fun stuff!

Great stuff indeed. The bottomline is, just do it. Maybe a batch or two and an idea of what I can achieve will help determine my needs.

I'm confident that the styles of beers I like I can manage with a 5-gallon. If not, I'll upgrade. I'm a flavor guy, not an alcohol guy. Bigs beers I've tried like Imperial Stouts and IPAs I didn't care for at all. I prefer pale ales, bitters, wit beers in the summer, porters, browns and stouts in the winter.

BTW, on my lunch just picked up the newest BYO. Good hops articles for those interested.

I have both the 5 gal (started with it and quickly found it was too small for many brews) and the 10 gal. I now used the 5 gal as my HLT. The most I've fit in the 5 was 12.5 lbs with a thick (1 quart/lb) mash, literally to the top...then I put the lid on, and I had a messy spill over. You can mash 11 pounds easily...more and you may encounter issues.